Fix module load errors for test_ari_model.so.

You cannot use a function pointer variable with an external function from
another dynamically loaded module because data variables are always
resolved even with RTLD_LAZY.

* Added wrapper functions for ast_ari_validate_int() and
ast_ari_validate_string() to use instead for the function pointer
variable.

(closes issue ASTERISK-22457)
Reported by: David M. Lee
........

Merged revisions 399207 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@399208 65c4cc65-6c06-0410-ace0-fbb531ad65f3